Multicasting is a communication technique permitting a single transmission device to transmit to a plurality of receiving devices. It differs from broadcasting over a radio air interface by, for example, defining specific recipients as group members in contrast to broadcast media. It often uses a wired network to transmit from a single transmission source device to a designated group of receiving devices. Being different from traditional broadcasting, the advent of multicast presents the opportunity to exploit its medium in many ways to permit development of advantageous features not available in the traditional broadcast medium.
Multicasting in a network setting simultaneously sends messages to a selected group of receiving (i.e., PCs; workstations, etc.) stations. The network may comprise, in-part or in-total separately or in combination, a telephone network; an Internet network; a LAN, a WAN and other similar arrangements. Multicast transmissions, from a network termination point to a host receiver device, of a receiving group, are subject to IGMP (Internet Group Management Protocol) standards. Examples of network termination points, to which a group of host receivers may be connected, are edge routers; gateways and other edge devices located in an IP network point-of-presence, etc.
IGMP is a protocol that is used to provide group membership data to neighboring multicast routers at the edge of a network. Recipient hosts are individually queried as to the membership group that they belong to and each provides leave group messages when a host wishes to leave a multicast session. A purpose of these queries is to insure that only group end hosts receive the multicast sessions. IGMP is only a subset of existing IP protocols but it is essential in order for the multicast session to work. While supposedly dealing with a group of recipient hosts its queries are generally individually received by all recipient host stations of that group. The last active station of a group sends notice that it is ending its multicast session and the multicast source ceases transmissions to the now inactive group. IGMP is currently in version 2, but a version 3 is presently being developed. A typical header of an IGMPv2 is shown in the FIG. 1.
It is desirable to obtain new advantages from attributes that the multicast system presents to the network (i.e., source content provider) provider. Many advantages are desirable but may not conform to existing IGMP protocol standards. In other instances such advantages may not conform to capabilities of existing equipment. It is desirable that any new features conform to existing IGMP and IP standards and network equipment.